NAME

usb_pipe_open, usb_pipe_xopen — Open a USB pipe to a device

SYNOPSIS

#include <sys/usb/usba.h>

int
usb_pipe_open(dev_info_t *dip, usb_ep_descr_t *endpoint, usb_pipe_policy_t *pipe_policy, usb_flags_t flags, usb_pipe_handle_t *pipe_handle);

int
usb_pipe_xopen(dev_info_t *dip, usb_ep_xdescr_t *extended_endpoint, usb_pipe_policy_t *pipe_policy, usb_flags_t flags, usb_pipe_handle_t *pipe_handle);

INTERFACE LEVEL

illumos DDI specific (illumos DDI)

PARAMETERS

dip: Pointer to the device's dev_info structure.
endpoint: Pointer to endpoint descriptor.
extended_endpoint: Pointer to an extended endpoint descriptor retrieved from calling usb_ep_xdescr_fill(9F).
pipe_policy: Pointer to pipe_policy. pipe_policy provides hints on pipe usage.
flags: USB_FLAGS_SLEEP is only flag that is recognized. Wait for memory resources if not immediately available.
pipe_handle: Address to where new pipe handle is returned. (The handle is opaque.)

DESCRIPTION

A pipe is a logical connection to an endpoint on a USB device. The usb_pipe_xopen() function creates such a logical connection and returns an initialized handle which refers to that connection.

The USB 3.0 specification defines four endpoint types, each with a corresponding type of pipe. Each of the four types of pipes uses its physical connection resource differently. They are:

Control Pipe: Used for bursty, non-periodic, reliable, host-initiated request/response communication, such as for command/status operations. These are guaranteed to get approximately 10% of frame time and will get more if needed and if available, but there is no guarantee on transfer promptness. Bidirectional.
Bulk Pipe: Used for large, reliable, non-time-critical data transfers. These get the bus on a bandwidth-available basis. Unidirectional. Sample uses include printer data.
Interrupt Pipe: Used for sending or receiving small amounts of reliable data infrequently but with bounded service periods, as for interrupt handling. Unidirectional.
Isochronous Pipe: Used for large, unreliable, time-critical data transfers. Boasts a guaranteed constant data rate as long as there is data, but there are no retries of failed transfers. Interrupt and isochronous data are together guaranteed 90% of frame time as needed. Unidirectional. Sample uses include audio.

The type of endpoint to which a pipe connects (and therefore the pipe type) is defined by the bmAttributes field of that pipe's endpoint descriptor. (See usb_ep_descr(9S)).

Prior to the USB 3.0 specification, only the usb_ep_descr(9S) was required to identify all of the attributes of a given pipe. Starting with USB 3.0 there are additional endpoint companion descriptors required to open a pipe. To support SuperSpeed devices, the new usb_pipe_xopen() function must be used rather than the older usb_pipe_open() function. The usb_ep_xdescr(9S) structure can be automatically filled out and obtained by calling the usb_ep_xdescr_fill(9F) function.

Opens to interrupt and isochronous pipes can fail if the required bandwidth cannot be guaranteed.

The polling interval for periodic (interrupt or isochronous) pipes, carried by the endpoint argument's bInterval field, must be within range. Valid ranges are:

Full speed: range of 1-255 maps to 1-255 ms.

Low speed: range of 10-255 maps to 10-255 ms.

High speed: range of 1-16 maps to (2**(bInterval-1)) * 125us.

Super speed: range of 1-16 maps to (2**(bInterval-1)) * 125us.

Adequate bandwidth during transfers is guaranteed for all periodic pipes which are opened successfully. Interrupt and isochronous pipes have guaranteed latency times, so bandwidth for them is allocated when they are opened. (Please refer to Sections 4.4.7 and 4.4.8 of the USB 3.1 specification which address isochronous and interrupt transfers.) Opens of interrupt and isochronous pipes fail if inadequate bandwidth is available to support their guaranteed latency time. Because periodic pipe bandwidth is allocated on pipe open, open periodic pipes only when needed.

The bandwidth required by a device varies based on polling interval, the maximum packet size (wMaxPacketSize) and the device speed. Unallocated bandwidth remaining for new devices depends on the bandwidth already allocated for previously opened periodic pipes.

The pipe_policy parameter provides a hint as to pipe usage and must be specified. It is a usb_pipe_policy_t which contains the following fields:

uchar_t         pp_max_async_reqs:

The pp_max_async_reqs member is a hint indicating how many asynchronous operations requiring their own kernel thread will be concurrently in progress, the highest number of threads ever needed at one time. Allow at least one for synchronous callback handling and as many as are needed to accommodate the anticipated parallelism of asynchronous* calls to the following functions: usb_pipe_close(9F), usb_set_cfg(9F), usb_set_alt_if(9F), usb_clr_feature(9F), usb_pipe_reset(9F), usb_pipe_drain_reqs(9F), usb_pipe_stop_intr_polling(9F), and usb_pipe_stop_isoc_polling(9F).

Setting to too small a value can deadlock the pipe. Asynchronous calls are calls made without the USB_FLAGS_SLEEP flag being passed. Note that a large number of callbacks becomes an issue mainly when blocking functions are called from callback handlers.

The control pipe to the default endpoints (endpoints for both directions with addr 0, sometimes called the default control pipe or default pipe) comes pre-opened by the hub. A client driver receives the default control pipe handle through usb_get_dev_data(9F). A client driver cannot open the default control pipe manually. Note that the same control pipe may be shared among several drivers when a device has multiple interfaces and each interface is operated by its own driver.

All explicit pipe opens are exclusive; attempts to open an opened pipe fail.

On success, the pipe_handle argument points to an opaque handle of the opened pipe. On failure, it is set to NULL.

CONTEXT

May be called from user or kernel context regardless of arguments. May also be called from interrupt context if the USB_FLAGS_SLEEP option is not set.

RETURN VALUES

USB_SUCCESS: Open succeeded.
USB_NO_RESOURCES: Insufficient resources were available.
USB_NO_BANDWIDTH: Insufficient bandwidth available. (isochronous and interrupt pipes).
USB_INVALID_CONTEXT: Called from interrupt handler with USB_FLAGS_SLEEP set.
USB_INVALID_ARGS: dip and/or pipe_handle is NULL. Pipe_policy is NULL.
USB_INVALID_PERM: Endpoint is NULL, signifying the default control pipe. A client driver cannot open the default control pipe.
USB_NOT_SUPPORTED: Isochronous or interrupt endpoint with maximum packet size of zero is not supported.
USB_HC_HARDWARE_ERROR: Host controller is in an error state.
USB_FAILURE: Pipe is already open. Host controller not in an operational state. Polling interval (Bep_descr bInterval field) is out of range (intr or isoc pipes).
The device referred to by dip is at least a SuperSpeed device and the older usb_pipe_open() function was used.

EXAMPLES

usb_ep_data_t *ep_data;
usb_ep_xdescr_t ep_xdescr;
usb_pipe_policy_t policy;
usb_pipe_handle_t pipe;
usb_client_dev_data_t *reg_data;
uint8_t interface = 1;
uint8_t alternate = 1;
uint8_t first_ep_number = 0;

/* Initialize pipe policy. */
bzero(policy, sizeof(usb_pipe_policy_t));
policy.pp_max_async_requests = 2;

/* Get tree of descriptors for device. */
if (usb_get_dev_data(dip, USBDRV_VERSION, &reg_data,
    USB_FLAGS_ALL_DESCR, 0) != USB_SUCCESS) {
        ...
}

/* Get first interrupt-IN endpoint. */
ep_data = usb_lookup_ep_data(dip, reg_data, interface, alternate,
    first_ep_number, USB_EP_ATTR_INTR, USB_EP_DIR_IN);
if (ep_data == NULL) {
        ...
}

/* Translate the ep_data into the filled in usb_ep_xdescr_t */
if (usb_ep_xdescr_fill(USB_EP_XDESCR_CURRENT_VERSION, dip,
    ep_data, &ep_xdescr) != USB_SUCCESS) {
       ...
}

/* Open the pipe.  Get handle to pipe back in 5th argument. */
if (usb_pipe_open(dip, &ep_data.ep_descr
    &policy, USB_FLAGS_SLEEP, &pipe) != USB_SUCCESS) {
        ...
}